https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94081
Bug ID: 94081
Summary: -Waddress-of-packed-member doesn’t take variable
attributes or __builtin_assume_aligned into account
Product: gcc
Version: 9.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: felix.von.s at posteo dot de
Target Milestone: ---
In this code:
#include <stdint.h>
struct foo {
uint16_t a, b;
} __attribute__((packed));
extern struct foo *f(void);
extern void g(uint16_t *p);
void h(void) {
struct foo *s0 = __builtin_assume_aligned(f(), 16);
g(&s0->a);
struct foo s1 __attribute__ ((aligned(16)));
g(&s1.a);
}
GCC will warn about taking the address of s0->a and s1.a, even though it has
enough information to recognise those as false positives.
On many platforms, variables on the stack are naturally aligned at a 32-bit
boundary, so I believe &s1.a is a false positive on those platforms as well,
but I’m less sure if skipping the warning for this case is desirable.
